1. Field of the Invention
The present invention relates to a color converting device that performs, when a first image processing device performs emulation for color reproduction using a second image processing device, color conversion for an image signal used in the first image processing device. The present invention also relates to a method for such emulation and a method of generating a three-dimensional lookup table used in the color conversion for the emulation. Moreover, the present invention relates to an image processing device including the three-dimensional lookup table for the emulation.
2. Description of the Related Art
As a patent document related to the present invention, there is JP-A-2006-19937.
In order to realize color reproduction between different kinds of devices or different kinds of media, it is necessary to correct a difference in a color range, i.e., a gamut, between input and output devices. A technique for the correction is called gamut conversion or gamut compression. For example, as a display output device that performs image display, there are a CRT (Cathode Ray Tube), a projector, a liquid crystal panel, and the like. As the projector, there are various projectors such as projectors of so-called DLP system and SXRD system and a film projector. As the liquid crystal panel, there are various liquid crystal panels such as a liquid crystal panel of an LED (Light Emitting Diode) backlight system. These display output devices have different gamuts as gamuts reproducible by the display output devices.
For example, in FIG. 21, a difference among gamuts of devices A to E, which represent the various display output devices, is shown as an XYZ chromaticity diagram.
Since the reproducible gamuts are different depending on the devices, for example, in order to cause a certain display output device to display a certain image signal, it is necessary to correct the image signal to be suitable for a gamut corresponding to the display output device.
When conversion of a gamut (compression of a gamut) is performed, it is a general practice to convert a color space with reference to a three-dimensional lookup table.
For example, as shown in FIG. 22, a three dimensional lookup table of a square cube having R, G, and B as axes (in the following explanation, lookup table may be referred to as “LUT” and three-dimensional lookup table may be referred to as “3DLUT”) is conceivable. In this 3DLUT, R, G, and B values inputted are divided into seventeen coefficient points (lattice points of a 3D skeleton) on the axes, respectively, to form a table of 17×17×17 conversion table coefficients. There are 4913 (17×17×17) lattice points marked by black circles. Output R, G, and B values or coefficient values for deriving the output R, G, and B values are stored in the respective lattice points. In other words, an output RGB value is calculated from an input RGB value with reference to a certain lattice point.
An output value of an axis or a lattice point of the 3DLUT is not limited to an RGB value but may be values of other colorimetric systems.